Bioprinting, or making living tissue with a three-dimensional printer, is a relatively new field. Because no one has come up with a perfect process, every group of scientists uses a slightly different method. Jonathan Butcher’s lab at Cornell University focuses on aortic valves, hoping to someday print replacement valves for children with heart disease.

Take an image

An MRI or CT scan or other 3-D image provides the exact dimensions of the tissue that is being replaced. Ideally the tissue will fit so well that the surgeon who implants the tissue will need to do very little, if any, modification.

Generate a blueprint

Computer design software uses the image to generate a detailed, layer-by-layer file that tells the printer where to place each type of cell material. To avoid reproducing defects, an expert may need to tweak the file before printing.

Make the “ink”

Living cells — ideally the patient’s own — are mixed into cell-friendly material, such as collagen, that will make a scaffolding for cells to grow on. The type of cells depends on what they need to do (muscle cells, blood vessel cells, etc.). Scientists can include environmental cues that encourage the cells to do certain things, such as prompting fibrous tissue to attach to muscle.

The first bioprinters were jury-rigged desktop inkjet printers. Now, some labs use machines, made specifically for bioprinting, that cost up to $300,000. Cornell labs make multipurpose 3-D printers, which cost about $2,000, and modify them for bioprinting.

How bioprinting works

Bioprinting, or making living tissue with a three-dimensional printer, is a relatively new field. Because no one has come up with a perfect process, every group of scientists uses a slightly different method. Jonathan Butcher’s lab at Cornell University focuses on aortic valves, hoping to someday print replacement valves for children with heart disease.

How bioprinting works in his lab:

Print

The printer deposits the living cell material in thin layers of usually 1/2 mm or less, although different nozzles can deposit larger or smaller amounts depending on the tissue being printed. The material comes out of the nozzles as viscous liquid, about the consistency of gel toothpaste.

Solidify each layer with UV light

Each layer starts as a liquid, but the tissue needs to firm up and hold its shape before more layers land on top. This blending and solidifying is called crosslinking. Butcher’s lab uses ultraviolet light to promote crosslinking because it works almost instantly. Other labs use heat or chemicals, which require more time between layers.

Incubate the new tissue

Scientists hope to be able one day to print some types of replacement parts directly into patients’ bodies. For now, tissues must spend a few weeks maturing in a type of incubator called a bioreactor. It does a sort of test drive, pushing blood through a heart valve, for example, or stretching muscle fibers, or sending fluid through a liver.

When will humans get bioprinted parts?

No bioprinted products have been put into human trials yet, but some are much closer than others. Several experts in the field helped compile this very loose timetable: